0 teutonico-lab manual


Published on

  • Be the first to comment

  • Be the first to like this

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

0 teutonico-lab manual

  2. 2. CONTENTS Foreword v Preface vii General Principles: Laboratory Science 1. Sampling 3 2. Measurement and Error: Precision, Accuracy, Statistics 7 3. Measurement: Mass (Use of the Balance) 11 4. Measurement: Length (Use of the Vernier Caliper and Micrometer) 16 5. Measurement: Volume 21 6. Measurement: Solutions 26 7. Measurement: pH 30 Porous Building Materials 8. Water Absorption by Total Immersion 35 9. Water Drop Absorption 41 10. Penetration of Water: Capillary Action 43 11. Porosity of Granular Beds 45 12. Porosity in Solids: Indirect Measurement by Water Absorption 50 13. Porosity in Solids: Hydrostatic Weighing 52 14. Movement of Salts 56 15. Salt Crystallization 57 16. Qualitative Analysis of Water-soluble Salts andThis publication was printed with a generous Carbonates 58contribution from the government of 17. Semiquantititive Analysis of Water-soluble Salts 68Finland. Earthen Building Materials 18A. Particle Size Analysis: Part I Sieving Procedure 73ISBN 92-9077-083-XVia di San Michele 1300153 Rome RM, ItalyPrinted in Italy III
  3. 3. Earthen Building Materials (continued) FOREWORD18B. Particle Size Analysis: Part II Sedimentation Procedure: Hydrometer Method 8319. Plastic Limit of Soils 96 After his appointment as director of ICCROM in 1977, Sir Bernard FEILDEN proposed to emphasize the interdisciplinary20. Liquid Limit of Soils 102 character of conservation by introducing scientists to field work and architects to laboratories. Consequently it was decided to introduce a series of laboratory exercisesStone. Brick and Mortars designed for the needs of architectural conservators and conservation architects in the program of the International21. Mortar Analysis: Simple Method 113 Architectural Conservation Course at ICCROM.22. Analysis of Calcium Carbonate Content in The present publication can be seen as an outcome of this Mortars: Calcimeter Method 117 initiative. It should be conceived as an introduction to the work in an architectural conservation laboratory, aimed at23. Mixing Mortars for Conservation 119 helping the reader to understand the character and behavior of building materials, their identification, and the24. Cleaning Building Stone 123 diagnosis of their state of conservation. It is believed that this manual would be useful not only to courses in25. Repointing of Stone and Brickwork 127 conservation, but also to schools of architecture and engineering, as well as institutions interested in26. Investigation of the Carbonation Process in establishing a low-cost architectural conservation Lime Mortars by Means of Phenolphthalein 129 laboratory. The material included has been drawn from different sources,Architectural Surfaces: and thanks are due to the many ICCROM lecturers and experts Renders. Plaster (Intonaco). Paint who have contributed to it. The training programs of the Scientific Principles of Conservation Course, run at ICCROM27. Sampling of Architectural Surface Materials 137 under the direction of Giorgio TORRACA, and the Istituto Centrale del Restauro in Rome provided a basis. The first28. Imbedding a Sample for Cross Section 139 selection and preparation of exercises was undertaken by Simonetta PERONI, then assistant to the Architectural29. Cutting and Polishing a Cross Section of Conservation Course. Since 1984, this material has been Surface Material; Observation of the Sample 143 completely revised, expanded, further elaborated and edited by Jeanne Marie TEUTONICO, who has dedicated much time to the30. Simplified Method for Imbedding and Polishing development of laboratory training in the Architectural a Cross Section of Plaster or Paint 148 Conservation Course at ICCROM. She has been assisted by Cynthia ROCKWELL and Monica GARCIA in the editing and publication of the manual, and by Mehr Azar SOHEIL in the lineWood drawings and graphic presentation.31. Wood Structure 155 Special thanks are due to the Finnish Government whose financial contribution made the publication of this manual-a32. Swelling and Shrinkage of Wood 158 reality.33. Cross Sections and Identification of Wood 16134. Test Loading of Wood 163 Dr Jukka Jokilehto Coordinator of35. Preparation and Application of Traditional Architectural Programs Oil House Paint 167iv v
  4. 4. PREFACEThis manual is intended to provide a basic introduction to the analysesof building materials that can be carried out in an architecturalconservation laboratory.Certainly, it is neither possible nor desirable to turn everyarchitectural conservator into a laboratory technician. The aim hereis to make architectural conservators more aware of the potentialoffered by the conservation laboratory for the understanding ofmaterials and structures. Such potential ranges from simple tests,which the conservator can conceivably carry out alone, to morecomplicated procedures for which the aid of a specialist might berequired. In either case, a greater familiarity with laboratory testsand techniques will better enable the architectural conservator toobtain the information needed for the critical evaluation of historicstructures.This manual has been prepared with such goals in mind. The presentedition is the result of four years of research, re-evaluation, andexperience in a teaching situation. It begins with a section on generalprinciples which provides an introduction to laboratory concepts,methods, and equipment. This is followed by a compendium of laboratoryanalyses and exercises, organized by building material. All of thesecan provide useful information with only simple equipment.The laboratory procedures have been collected from various standardizedsources (ASTM, NORMAL, RILEM, etc.) and then adapted by the author tosuit the specific needs of the architectural conservator. This processhas often necessitated a complete re-thinking and re-working of theparent methodologies. Too frequently, procedures are simply"transferred" from related disciplines (i.e. conservation of objectsor paintings) and have little relevance to the scale, materials,deterioration processes, and environmental conditions faced by thearchitectural conservator. Thus, though original sources ofexperiments have been cited in the bibliographic references, theresulting procedures sometimes bear little resemblance to theirorigins.In certain cases for which no standardized tests exist, the analyseshave been based on procedures developed by various conservation expertsor teaching laboratories (cited in the bibliographic references). Thesehave been similarly modified by the author to suit the aims and formatof the manual.It is important; to emphasize that the analyses contained in thiscompendium have been adapted to the exigencies of a basic conservationlaboratory. All are designed to give scientifically reliable resultswith simple and inexpensive equipment, thus respecting the economicrealities and working conditions of many architectural conservationprojects. vii
  6. 6. Ex. 1 SAMPLINGINTRODUCTION/AIMThis exercise introduces the sampling process and the variables thataffect it. It is important to remember that the experimental processbegins in the field when the samples are taken. As in the laboratory,experimental design (i.e. the sampling procedure) is critical. Theconservator must consider factors such as: WHEN should samples betaken? Under what conditions? Using which instruments? HOW MANYsamples should be taken? Of what size? WHERE should the samples comefrom? WHAT information is desired (i.e. why are the samples beingtaken)? It is essential to keep in mind that both techniques andresults must be reproducible.DEFINITIONS(1) Types of Comparison: The experimenter must gather enough data to make relevant comparisons. These can be external in which evidence about the subject building is compared with other buildings OR internal in which individual pieces of evidence are compared with the building as a whole. In general, internal comparisons are more reliable because very few procedures are standardized.(2) Types of Sampling: Random sampling: A process in which samples are chosen at random; spot-checking (e.g. quality control in factories). Non-random sampling: A process in which samples are drawn from a particular area or group (e.g. if deterioration on a building occurs in a localized area, all samples may be drawn from there if the purpose of the investigation is to discover the cause of deterioration). Population: The entire sample group.MATERIALS50 coins or chips; red nail polish; plastic bag; graph paper; notebook;calculator. 3
  7. 7. Ex. 1 (continued) Ex. 1 (continued)PROCEDURE Population: Marked coins ______________ Unmarked coins1. Work in teams of three persons: one person (R) to record the data and the others (El and E2) to collect the samples.2. Mark 5 of the coins with red nail polish.3. Place 5 marked and 45 unmarked coins in the plastic bag. Shake the bag to mix the coins.4. Let El reach into the bag and pull out a random quantity of coins from the bag. Let R record the number of marked and unmarked coins in the sample on the attached chart.5. Return the sample pulled by El to the plastic bag. Mix the coins and let E2 pull a random quantity of coins from the bag. Let R record the number of marked and unmarked coins in the sample on the attached chart.6. Repeat steps ( 4 ) and (5), alternating El and E2, until the ratio of marked/unmarked coins (keep a running total as indicated on the chart) equals or closely approximates the actual ratio of the population.7. Express the results mathematically by completing the chart.8. Express the results graphically showing the ratio as a function of the number of samples.9. Repeat the entire procedure using a sample population of 20 marked coins out of 50.DISCUSSION(A) How did the following factors affect the sampling results: 1) Actual composition of the population (actual ratio of marked to unmarked coins). 2) Number of coins in each sample (relationship of sample size to actual composition of the population). 3) The sample collector (compare El and E2). 4) The method of sample collection.(B) What were the possible sources of error?(C) What general statements can you make about the reliability of sampling and the factors that affect it?4 5
  8. 8. Ex. 2 MEASUREMENT AND ERROR: PRECISION, ACCURACY, STATISTICSEx. 1 (continued)Population: Marked coins____________ Unmarked coins_____________ AIM To become familiar with the standard statistical evaluation of data. This exercise is designed to introduce the concepts of precision and accuracy and to provide a basic framework for the mathematical manipulation of laboratory data. DEFINITIONS (1) Data Treatment: Much of a conservators data is numerical. These numbers must be (a) sorted and (b) questioned through statistics to arrive at some sort of assumption. In this regard, it is essential to understand the difference between precision and accuracy. Precision: Degree of agreement of repeated measurements of the same quantity. It is a statistical value, the calculation of which is described below. Precision and reproducibility are synonymous. Accuracy: The agreement between the result of a measurement and the true or real value of the quantity measured. (A measurement that is accurate is not only reproducible but also the "right" answer.) "Accuracy" has to do with the closeness (of data) to the truth, "precision" only with the closeness of readings to one another. (2) Calculations: Mean: The average. Sum up all the data and divide by the number of values. Mode: The most common piece of data. Median: The value right in the middle. The dispersion of data about the mean gives an idea of the precision of a series of measurements. There are several ways to measure dispersion, including: Range or Spread: The difference between the least and the greatest values in a set of data. Absolute Deviation: For each piece of data, the difference between its value and the mean. The difference may be positive (greater than the mean) or negative ,(smaller than the mean). This does not affect its "absolute value".6 7
  9. 9. Ex. 2 (continued)Ex. 2 (continued) EXAMPLE OF PRECISION CALCULATIONS Mean_Absolute _Deviation: An average of the absolute Results Absolute Deviations Square Deviations deviations of the sample data. Mean Relative Deviation: Mean Absolute Deviation Mean The _Standard Deviation: The most widely employed system. It establishes an interval in which at least 2/3 of the values will fall. Median = 17.1 Range = from 16.0 to 17.7 with a mean of 17.0; it is written 17.0 +0.7 -1.0 3 out of 5 results fall in this range. PROCEDURE Do the following exercise: The weight of a silver ring is measured 10 times on a rather large balance on which the weight may be measured up to 0.01 of a gram. The results are as follows: Calculation of Standard Deviation: First, calculate the Variance. This is the sum of all the squares of the absolute deviations divided by the number of values. The Standard_ _ Deviation (indicated by the Greek letter sigma δ) is the square root of the variance. u = mean x = individual item N = number of elements or, for small amounts of d ata , the Standard Deviation is: u = mean x = individual item x = individual item N = number of elements A. Fill in the chart.98 9
  10. 10. Ex. 2 (continued) Ex. 3 MEASUREMENT: MASS (Use of the Balance)B. Calculate the: AIMMean: Balances are mechanical devices used to determine the mass of objects.Median: Many kinds of balances are available, ranging from rough measuring devices which are sensitive to 0.1 g to the analytical balancesRange: sensitive to fractions of a microgram.Mean Absolute Deviation: The choice of a balance obviously depends upon its designated use. The following exercise introduces two balances typically used in theVariance: architectural conservation laboratory: a Sartorius single-pan, top-loading balance (precision 0.1 g, maximum load 1000 g), and aStandard Deviation: Mettler balance of a similar design (precision 0.01 g, maximum load 1200 g).C. Graph the results. DEFINITIONS Mass: An invariant measure of the quantity of matter in an object. The SI (International System of Units) unit of mass is the kilogram, but gram quantities are more usual in the laboratory. Technicians properly use the term mass in discussing measurements made with a balance. Weight: The forces of attraction exhibited between an object and the earth. Weight equals mass times the gravitational attraction. Mass is proportional to weight, so we ordinarily interchange the terms, but the unit of weight is the newton. Capacity: The largest load on one pan for which the balance can be brought to equilibrium. Readability: The smallest fraction of a division at which the index scale can be read with ease. Sensitivity: The change in load required to produce a perceptible change in indication. It is, therefore, a ratio and not to be used to discuss the quality of a measurement. Significant Figure: A digit that shows a quantity in the position that it occupies in the whole numerical term. A zero is not significant when it is used to locate the decimal point; it is significant, however, when it fixes quantity, for example, when it, indicates that the value is nearer to 0 than to 1. 1 y E.g. In the number 1.500 x 10 , the zeroes are, significant because they show that the quantity is nearer to 1.500 x 1 10 1 than to 1.501 x 10 1 or 1.499 x 10 . 1110
  11. 11. Ex. 3 (continued) Ex. 3 (continued) A number should contain no more than one doubtful digit. For a number such as 2.987 with four significant digits, only the 7 should be doubtful.PROCEDURE1. Examine the attached diagram of the Sartorius balance which outlines its parts and their use.2. Check the balance zero.3. Weigh the sample objects (A) given to you.Record the weights in Data Sheet 1.4. Weighing materials in a beaker: Procedure (a): Weigh the beaker empty (W 1 ). Place sample 2A in the beaker and weigh (W2). Subtract W1 from W2 to obtain the weight of the sample (W3). Record your results in Data Sheet 2. Procedure (b): Use the Tare knob on the balance. Place the beaker on the pan and turn the Tare knob until it reads zero. Place sample 2 in the beaker and weigh. Record the weight in Data Sheet 2. Are the weights obtained using procedure (a) and procedure (b) the same? What are the possible sources of error?5. Empty the pan of the balance. Return the Tare knob to zero.6. Lock the pan of the balance.7. Repeat Steps 1 through 6 using the Mettler balance and Samples 1B through 6B. -BIBLIOGRAPHYICCROM, Scientific Principles of Conservation Course, Courseexercises, 1976-77.Shugar, G. - Shugar, R. - Bauman, L. - Bauman, R.S. ChemicalTechnicians Ready Reference Handbook. New York: McGraw Hill, 1981.12
  12. 12. Ex. 3 (continued) Ex. 3 (continued) 1514
  13. 13. Ex. 4 MEASUREMENT: LENGTH (Use of the Vernier Caliper and Ex. 4 (continued) Micrometer) To measure with the vernier caliper:AIM 1. Close (or open) the jaws so that they very lightly clamp the object at the desired point of measurement.There are many types of laboratory tools for the precise measurement of 2. Read the fixed scale. The nearest scale division to the left of thelength. Among these are the vernier caliper and the micrometer or screw zero on the vernier indicates the number of whole millimeters beinggauge. The purpose of this exercise is to make you familiar with the care measured.and use of these instruments. 3. Read the vernier. The line of the vernier that directly coincides with a line on the fixed scale indicates the number of tenths (orDEFINITIONS twentieths) of a millimeter to be added. See the example below.Calipers: Calipers consist of a pair of hinged steel jaws which are used for measuring the dimensions, both internal and external, of small objects where a scale rule cannot be applied directly.Vernier scale: Invented by Pierre Vernier in the seventeenth century, the vernier scale is fitted to many types of measuring and surveying instruments. It enables measurements to be made by direct reading to 0.1 mm without having to estimate fractions of a division.Vernier calipers: Vernier calipers consist of a fixed steel scale marked in millimeters (from 16 to 20 cm in length) with a fixed jaw Vernier calipers have jaws for both internal and external measurements. at one end, and a sliding jaw carrying a scale (the vernier) They can also be used for depth measurement as indicated below. which is 9 mm long and divided into 10 (or 20) equal parts.
  14. 14. Ex. 4 (continued) Ex. 4 (continued)Micrometer or Screw Gauge: An instrument used for the measurement oflengths between 0.01 mm and a few centimeters. It is thus more 4. The length of the object is read by adding (a) the number ofsensitive than the vernier caliper but has a narrower range. Though millimeters and half millimeters indicated by the length of thethere are diverse types, a typical micrometer is illustrated below. fixed scale uncovered by the thimble and (b) the number on theThe range of this instrument (0-25 mm, 25-50 mm, 50-75 mm) is usually moving scale which most nearly coincides with the base line onindicated on the face of the U-shaped piece. the fixed scale. See examples below.To measure with the micrometer:1. Make sure the faces of the spindle and the anvil are clean and free of dust.2. Place the object to be measured in the mouth of the micrometer.3. Gently rotate the thimble until the object is lightly clamped between the anvil and the spindle (the thimble will stop moving). Make final adjustments with the ratchet knob. When the ratchet knob begins to slip round, you are ready to read the scales.18 19
  15. 15. Ex. 4 (continued) Ex. 5 MEASUREMENT: VOLUMEPROCEDURE1. Measure the samples given to you with the vernier caliper. AIM Record the dimensions below: There are many different types of laboratory equipment for measuring volume. This exercise is intended to make you familiar with the volumetric equipment most frequently used in the architectural conservation laboratory. DEFINITIONS Units of Liter (L): the volume occupied by one kilogram of Volume water at 4°C and standard atmospheric pressure; this volume is equivalent to one cubic decimeter. Milliliter (mL): one-thousandth of a liter. 3 Cubic centimeter (cm ): can be used interchangeably with milliliter without effect. Meniscus: The curvature exhibited at the surface of a liquid that is confined in a narrow tube such as a cylinder, buret, or pipet.2. Make sure the instrument is free from dust and return it to its case. It is common practice to use the bottom of the meniscus in calibrating and using volumetric glassware (see3. Using the micrometer, measure the second set of samples given illustration on page 22). to you. Record the results below VOLUMETRIC EQUIPMENT General Care: Only clean glass surfaces will support a uniform film of liquid; all volumetric glassware must there-fore be clean and free of grease. Water should flow continuously on the glass surface without leaving any drops.4. Make sure the micrometer is clean and return it to its case.5. Compare your results with those of others in the lab. What are the possible sources of error?BIBLIOGRAPHYHead, K.H. Manual of soil laboratory testing. London: Pen-techPress, 1980.ICCROM, Scientific Principles of Conservation Course, Coursenotes.Lucarelli, S. Notes on the use of measuring instruments. Rome:ICCROM, 1979.Shugar, G. - Shugar, R. - Bauman, L. - Bauman, R.S. Chemicaltechnicians ready reference handbook. New York: McGraw Hill, 1981. 2120
  16. 16. Ex. 5 (continued) Ex. 5 (continued)Cleaning: Volumetric glassware can normally be . cleaned by washing and brushing with a detergent solution. The cleaned glass ( c ) Pipet: This piece of volumetric equipment is designed for the should then be rinsed first with tap water and, finally, transfer of known volumes from one container to 4 or 5 times with distilled water. another. Pipets that deliver a fixed volume are called volumetric or transfer pipets (see below). Other (Stubborn dirt may be removed with chromic acid. The pipets, calibrated in convenient units so that any volume preparation and use of this reagent, however, is quite up to a maximum capacity can be delivered, are known as dangerous and should only be done by trained technicians.) measuring pipets. Volumetric glassware should be dried at room temperature Proper use of a transfer pipet (see diagram below): (i.e. on a rack), never in a hot oven which may alter calibration.Types of Glassware:(a) Graduated Cylinders: Perhaps the most common type of volumetric equipment. These range in size from 25 mL to 1000 mL. When using any graduated cylinder to measure a volume of liquid, remember to read the bottom of the meniscus. As shown below, it is important to have the eye at the same level as the meniscus to avoid parallax errors.(b) Volumetric Flask: A type of volumetric equipment calibrated to contain a specified volume when filled to the line etched on the neck.22 23
  17. 17. Ex. 5 (continued) Ex. 5 (continued)(d) Buret: Like the measuring pipet, this piece of volumetric equipment is designed to deliver any volume up to its maximum capacity. It is fitted with a stopcock for control PROCEDURE of liquid flow. The buret is most commonly used for 1. Become familiar with the various pieces of volumetric equipment titration processes. given to you. Titration: A process by which a substance to be measured 2. Practice reading the meniscus of the liquid volume in the graduated cylinder. is combined with a reagent and quantitatively measured. Ordinarily, this is accomplished by the controlled 3. Practice transferring a volume of liquid from one container to addition of a reagent of a known concentration to a another using the pipet. solution of the substance until the reaction between the two is judged to be complete. The volume of the reagent is then measured. 4. Prepare the solutions outlined in Exercise 6. BIBLIOGRAPHY ICCROM, Scientific Principles of Conservation Course, Course notes. Shugar, G. - Shugar, R. - Bauman, L. - Bauman, R.S. Chemical technicians ready reference handbook. New York: McGraw Hill, 1981.24 25
  18. 18. Ex. 6 MEASUREMENT: SOLUTIONS Ex. 6 (continued) AIM Volume Percent: Milliliters of solute per 100 milliliters of solution Most of the time, substances are not used pure. Instead, they (used in the case of mixing liquids; a v/v percent). are diluted in other substances to make solutions. This exercise will introduce you to various types of solutions and how to make E.g. 25 mL of acetone (1 part) diluted in 75 mL of them. H 2 O (3 parts) = 25 % by volume solution. Why? Volume of solute___ = __25 mL = 25 = 25 % DEFINITIONS Volume of solution 25 + 75 mL 100 Solution: A homogeneous system of two or more substances Molar and Molal Solutions: which may be present in varying amounts. To understand these types of solutions, one must first grasp the concept Solute: That substance which is dissolved or has gone of the mole. into solution (e.g. sugar into water). It constitutes less than 50 percent of the solution. One mole (also called the gram-molecular mass) is the number of grams equal to the molecular weight of a substance. The gram-molecular mass Solvent: That substance which does the dissolving (e.g. can be calculated by adding the individual atomic masses (see the water dissolving sugar).It constitutes more attached Periodic Table of Elements based on C = 12 g/mole*) of the than 50 percent of the solution. component parts of a molecule. Composition: Mass of solute per unit mass of solvent. E.g. to calculate the mass in grams of one mole of NaCl (table salt): Concentration: Amount of solute per unit volume of solvent. Na = 22.99 g/mole CALCULATIONS Cl = 35.45 q/mole NaCl = 58.44 g/mole There are many ways to express and prepare the concentration of * Since the Periodic Table of Elements has been standardized around laboratory solutions. These include: Carbon 12 at 12 g/mole, a mole of any element contains the same number of atoms. This number is called AVOGADROS NUMBER and equals 6.02 23 x 10 . Mass Percent: Grams of solute per 100 grams of solution (w/w*). Molality (m): The number of moles of solute per 1000 grams of solvent. E.g. 25 g of NaCl in 100 g of H 2 O . is a 20% by mass solution. This is a composition term. Why? Mass of solute = 25 q = 25 = 20% E. g. 58.44 g of NaCl dissolved in 1000 g of H 2 O is a lm solution. Mass of solution 25 g + 100 g 125 29.22 g of NaCl dissolved in 1000 g of H 2 O is a 0.5m solution. 3 * The density of water at 4 ° C is 1 g/cm = 1 g/mL. The terms milliliter and cubic centimeter (cc) are therefore usually interchangeable. One Molarity (M): The number of moles of solute per liter or 1000 mL of mL of water is also assumed to weigh approximately 1 gram (though solution. This is a concentration term. it varies somewhat according to the temperature). Thus, in the case of mass percent solutions where the solute is water, 100 g of water E.g. If 58.44 g of NaCl are dissolved in H 2 O and the volume of can be assumed equal to 100 mL of water. the solution is 1000 mL, it is a 1M solution. Molar concentrations are also indicated by square brackets. [HC1] = 1 means that a solution of HC1 is one molar. MOLARITY is probably the most common system for calculating the concentration of solutions.26 27
  19. 19. Ex. 6 (continued) Ex. 6 (continued)MATERIALS/EQUIPMENT Periodic Table of ElementsBalance, volumetric glassware (see Exercise 5), sodiumchloride, sodium sulfate, copper sulfate, alcohol, water.PROCEDURE1. Prepare 200 g of a 10 % by mass solution of NaCl in water.2. Prepare 200 mL of a 25 % by volume solution of alcohol in water.3. Prepare 100 mL of a 0.2M solution of copper sulfate (CuSO 4 . 5H 2 0) in water. - Calculate formula weight. − Weigh desired quantity of solute. − Transfer to volumetric flask; add water to line.4. Prepare 250 mL of a 0.2M solution of sodium sulfate (Na 2 SO 4 10H 2 O) in water. For preparing solutions of definite molarity, the formula is: molecular mass of compound x molarity wanted x number of liters = grams of compound needed to make solution.BIBLIOGRAPHYICCROM, Scientific Principles of Conservation Course, Course notes,1977.Shugar, G. - Shugar, R. - Bauman, L. - Bauman, R.S. Chemicaltechnicians ready reference handbook. New York: McGraw Hill, 1981.28 29
  20. 20. Ex. 7 MEASUREMENT: pH Ex. 7 (continued)AIM EQUIPMENT/MATERIALSIt is often important for an architectural conservator to know whether pH indicator strips, pH meter, various indicator solutions, variousa solution is acid, basic, or neutral. Such information is also test solutions, beakers, glass stirring rods, blotting paper.critical in the analysis of meteorological agents such as rain or snowwhich could cause decay of building materials if excessively acid or PROCEDUREalkaline (basic). The following experiment aims to explain the conceptof pH and its measurement. 1. Using the pH strips, measure the pH of the solutions given to you. Record your results on the table below.DEFINITIONS (Refer to BIBLIOGRAPHY for complete information). A 2. Repeat this procedure using the electronic pH meter. Record your results on the same table.solution is:Acid if there are more hydrogen ions than hydroxyl ions.pH is a value that represents the acidity or alkalinity of a solution. It is defined as the logarithm of the reciprocal of [H + ]. − A very acid solution has a pH of 1 (e.g. 0.1M HC1). − A very basic solution has a pH of 14 (e.g. 1M caustic soda). − A neutral solution has a pH of 7.A buffer solution is one that tends to remain at a constant pH. 3. Check the pH range of the indicators given to you by adding a drop of the sample solutions of varying pH. Note color changes.MEASUREMENTSThe pH of a solution may be measured in three ways: BIBLIOGRAPHY 1) By means of indicator solutions , that is by dyes that change color ICCROM, Scientific Principles of Conservation Course, Course notes, at a given pH (see attached table). 1977. 2) With pH test paper or "strips". These are commercially available Shugar, G. - Shugar, R. - Bauman, L. - Bauman, R.S. Chemical paper strips which have been impregnated with an indicator (test technicians ready reference handbook. New York: McGraw Hill, 1981. papers are available for every value of pH). The strip is wet with Torraca, G. Solubility and solvents for conservation problems. the solution to be tested and immediately compared with the standard Rome: ICCROM, 1975. color chart provided for each paper and range. The pH can be visually determined by comparison of colors. 31 3) With an electronic device known as the pH-meter. 30
  22. 22. Ex. 8 WATER ABSORPTION BY TOTAL IMMERSIONAIMThe measurement of water absorption is a useful laboratory test tocharacterize porous building materials, to evaluate the degree ofdeterioration, and to monitor the effects of conservation treatments.This exercise presents a simple method for such measurement which givesreliable results without sophisticated equipment.DEFINITIONSWater Absorption by Total Immersion: The quantity of water absorbed by a material immersed in deionized water at room temperature and pressure, expressed as a percentage of the dry mass of the sample.Water Absorption Capacity: The maximum quantity of water absorbed by a material under the cited conditions, again expressed as a percentage of the dry mass of the sample.EQUIPMENTOven, dessicator, balance, plastic trays, cloth, glass stirring rods,silica gel, deionized water.PROCEDURE1. Samples should be of regular form: cubes, cylinders or parallelepipeds. In the case of cubes, the side should not be less than 3 cm nor greater than 5 cm, so that the value of the ratio s/v (surface to apparent volume of the sample is between 2 and 1.2). Wash the samples in deionized water before beginning the test in order to eliminate powdered material from the surface. The number of samples required depends on the heterogeneity of the material being tested. In general, a series of at least three samples is recommended. These should be as similar as possible in terms of physical properties and condition.2. Dry the samples in an oven for 24 hours at 60°C; this relatively low drying temperature will prevent the deterioration of any organic substances employed in the case of treated samples. After drying, place the samples in a dessicator with silica gel to cool. 35
  23. 23. Ex. 8 (continued) Ex. 8 (continued)3. Weigh (M 0 ) the samples. Repeat the drying process until the mass CALCULATIONS of the sample is constant; that is, until the difference between 2 successive weighings, at an interval of 24 hours, is not more 1. Using the data you have recorded, calculate the mean value of the than 0.1 % of the mass of the sample. water absorption (the sum of all values for WA divided by the number of samples) at each time interval. Express the results numerically in Data Sheet 2 and in graph form as a function of time (Graph 1).4. Once the samples have been completely dried and the constant mass recorded, place them in a tray; preferably on supports (for 2. Again, using the figures from Data Sheet 1, calculate the Water example, glass stirring rods), and slowly pour deionized water Absorption Capacity (WAC) with the following formula: into the tray until the samples are totally immersed and covered by about 2 cm of water.5. At chosen intervals of time, take each sample out of the water, blot quickly with a damp cloth to eliminate surface moisture, and then weigh. Record the value obtained in the data sheet. Re-immerse the sample in water. : M6. The choice of the intervals of time during the first 24 hours is where max= the mass of the sample at maximum dependent on the absorption characteristics of the materials: water absorption a) Stone and brick should be weighed after the first 5 minutes of immersion and then every hour for the- first 3 hours. M d = the mass of the sample after redrying at the b) Mortar samples should be weighed a few minutes after termination of the test (see step 8). immersion, and then at increasing intervals (15 min, 30 min, 1 hour, etc.) for the first 3 hours. Record the result obtained in Data Sheet 2. All samples should then be weighed at 8 hours from the beginning of the test and then every 24 hours until the quantity of water absorbed in two successive weighings is not more than 1 % of the DISCUSSION total mass. Compare your numerical results and graphics with those of other lab7. At each interval, the quantity of water absorbed (WA) with groups. respect to the mass of the dry sample is expressed as: Which materials absorbed more water? where M n = weight of the wet sample at time t n M o = weight of the dry sample Which materials absorbed water at a faster rate? When was the highest percentage of water absorbed for each material? What factors do you think influence the varying water absorption capacities of each material? Record these values for water absorption in Data Sheet 1. What are the possible sources of error in this experiment?8. At this point, take the samples out of the water and dry them again in an oven at 60°C until they have reached constant mass (see steps BIBLIOGRAPHY 2 and 3). Record this value (M d ) in the data sheet. Proceed to the Calculations. Italian NORMAL Committee. NORMAL 7/81. Assorbimento dacgua per immersione totale; capacità di imbibizione. Rome: CNR, ICR, 1981. 3736
  25. 25. Ex. 8 (continued) Ex. 9 WATER DROP ABSORPTIONGRAPH 1: WATER ABSORPTION CURVE / MEAN VALUES AIM This exercise presents a simple method for the measurement of changes in the properties of stone surfaces caused either by treatment with hydrophobic (water repellent), consolidating, or hygroscopic materials, or by weathering. The measurement of water drop absorption is therefore a laboratory test for both treated and untreated stone. It is especially appropriate for determining the water repellency of stone surfaces. DEFINITIONS Water drop absorption rate: the absorption time of a limited and definite amount of water by the surface of a material. EQUIPMENT Oven, dessicator, common laboratory buret, deionized water. PROCEDURE 1. Take treated and untreated samples and dry them in an oven at 60°C for 24 hours (or until the difference between two successive weighings is not more than 0.1 % of the mass of the sample). Allow the samples to cool at room temperature. 2. Place the buret, filled with deionized water, at a distance of 1 cm from the sample surface. 3. Drip 1 mL of water onto the horizontal sample surface. 4. The time required for the total absorption of the water is determined as (t x ) for treated or weathered samples, (t n ) for untreated or unweathered reference samples. 5. Determine the evaporation time (t e ) of the drop during the measurement procedure by dripping 1 mL of water onto an analogous rough glass surface. 6. Expression and interpretation of results: If treated samples exhibit longer absorption times in relation to those of reference samples, this indicates a reduction of stone, porosity by a consolidating treatment, or a water repellettcy of .the surface caused by a hydrophobic impregnation. Totally water-repellent surfaces do not absorb water; in this case, the time in which the drop disappears is equal to its evaporation time (t e ). 4140
  26. 26. Ex. 9 (continued) Ex. 10 PENETRATION OF WATER: CAPILLARY ACTIONIf treated samples exhibit shorter absorption times inrelation to those of the reference samples, this indicates AIMan increase in the stone porosity caused by weathering ora hygroscopicity of the surface induced by hygroscopic Water is almost always a principal cause of the deteriorationimpregnation. of porous materials. The movement of water is related to the physical characteristics of the material such as itsIn order to be compared, the absorption times measured on structure, porosity, capillarity, and permeability. The maindifferent samples of stone must be transformed onto a sources of water are rain, condensation, and capillarity.relative scale. The following equations have been found to This simple experiment simulates the action of rising dampprovide a useful scale for figures: by capillarity.The water drop absorption (WA) of treated and weathered EQUIPMENTsurfaces is calculated as a percentage (the absorption of Tray, ruler, water.the reference untreated surfaces being set equal to 100%): PROCEDURE 1. Place a brick upright in a container as indicated in Fig. 1. Add water to the container until 1 cm of the base of the brick is immersed. 2. Measure the height ( H ) of the rising damp every minute for the first 5 minutes, then every 5 minutes for the next 25 minutes, then every 30 minutes. Record the results below.BIBLIOGRAPHYUnesco, RILEM. Water drop absorption. In: Deteriorationand protection of stone monuments: experimental methods.Volume V, Test II.8b. International Symposium, Unesco,Paris, 1978.42 43
  27. 27. Ex. 10 (continued)3. Draw a graph with the data obtained: Ex. 11 POROSITY OF GRANULAR BEDS Height (H) versus (t) as in Fig. 2 and height (H) versus the square root of time as in Fig. 3. AIM The aim of this test is to measure the total porosity of a granular material by means of its apparent and real densities (the latter obtained by a fluid displacement method). DEFINITIONS Porosity E: The fraction of the total volume of a solid that is occupied by pores (more simply, the empty spaces or voids in a solid mass). The % Porosity = % Voids. Permeability: The ability to transmit liquid or gas from one place to another. Capillarity: The attraction between molecules, both like and unlike, which results in the rise of a liquid in small tubes or fibers or in the wetting of a solid by a liquid. Porosimetry: The study of pore-size distribution. The volumetric distribution of the open pores, assumed to be of circular section, according to their size (radius or diameter), usually expressed as a per- centage of the mass of the sample. This property is related to capillarity, which increases in inverse proportion to the pore diameter (i.e. capillarity is greater where there are smaller pores). Apparent Volume (Va): The volume of a sample including the pore space. Real Volume (Vr): The apparent volume of the sample minus the volume of its pore space accessible to water. Apparent Density (pa): The ratio of the mass to the apparent volume of the sample expressed in kg/m3. Real Density (pr): The ratio of the mass to the real (or impermeable) volume 3 of the sample expressed in kg/m . BIBLIOGRAPHY Principle of Archimedes: If a solid body is wholly or partially immersed Massari, G. Humidity in monuments. Rome: ICCROM, 1971. in a liquid, the upthrust force (or buoyancy force) acting on the body is equal to the weight force of the liquid displaced Mora, P. Causes of deterioration of mural paintings. Rome: by the body, and acts vertically upwards through the center ICCROM, 1974. of gravity of the displaced liquid. The apparent mass of a solid body immersed in water is therefore equal `to the mass of the body less the mass of water displaced. When a body floats in water, the mass of water displaced is equal to the mass of the body, whether it is totally or partially immersed. 44 45
  28. 28. Ex. 11 continued) Ex. 11 (continued)CALCULATIONS EQUIPMENTPorosity ε is generally calculated by means of the following Oven, balance sensitive to 0.1 g, graduated cylinder, sampleformula: containers. PROCEDURE 1. Weigh the sample container (M c ). ° P a = apparent density as defined above AND 2. Place granular sample A (previously dried in the oven at 60 C ° ± 5 C for 24 hours) in the sample container and weigh (M l ). P r = real density as defined above. M l - M c = Mass of sample (M s ).The formula is derived in the following way: 3. Calculate the apparent volume (V a ) of the sample by placing it in the graduated cylinder. Since for practical purposes 1 mL = 3 1 cm the volume of the sample can be read directly from the cylinder scale. (Obviously, your reading will change depending on how closely packed the sand particles are. Shake the cylinder a few times to strike a reasonable balance between the densest and loosest compaction states.) 4. From the data obtained in Steps 2 and 3, calculate the apparent density (pa): Record all values on the attached data sheet. 5. Next, calculate the real volume of the sample by placing it in a cylinder containing a known volume of water. The amount of water displaced is equal to the real volume (V r ) . 6. Calculate the real density (p r ): Record these values on the attached data sheet. 7. From the values obtained in Steps 4 and 6, calculate the % Porosity (%, ε ) for the sample: 8. Repeat the above procedure for each of the granular samples. Record all results on the data sheet. 47 46
  29. 29. Ex. 11 DATA SHEETEx. 11 ( c o n t i n u e d )DISC USS ION− Can yo u d ra w a ny con cl usio ns ab ou t t he r e l a t i o n s h i p of grai n s i z e to p o r o s i t y ?− Was t her e a ny n o t i c e a b l e d i f f e r e n c e b etwe en th e p o r o s i t y of th e sam p les o f hom o gene ous gra in s i z e and thos e of m ixed p a r t i c l e s i z e s ? Ca n yo u dra w any co ncl u sion s abo u t t he r e l a t i o n s h i p be twe en p o r o s i t y and po ros i metr y? be t ween porosity and per me abil ity ? betw een p oros ime try and perm eab ili ty?− What a re th e p o s s i b l e sour ces o f erro r in th is exp eri me nt?BIBL IOG RAP HYColu mbi a U n i v e r s i t y , Pr og ram in HistoricPreservation,Cons erv ati on S cie nce Cou rse , L abor ato ry e x e r c i s e s , 198 3.R o s s i - D o r i a , P a o l a . Some la bor ator y t e s t s on st one . C ours enote s for the IC CRO M S c i e n t i f i c P r i n c i p l e s of Co n serv ati onCour se, 19 83.48 49
  30. 30. Ex. 12 POROSITY IN SOLIDS: INDIRECT MEASUREMENT BY WATER ABSORPTION Ex. 12 (continued)AIM DISCUSSIONThis exercise offers a simple method for the approximate measurement − What conclusions can you draw about the relationship between waterof porosity in solids. It can be viewed as a follow-up to Exercise 8: absorption capacity and porosity?Water Absorption by Total Immersion. − Which of the materials tested was most porous? Which was least porous? How do you think these values would affect the weatherability of the material under varying climatic conditions?PROCEDURE How would they influence the effectiveness of certain conservation treatments?Using the data obtained in Exercise 8, estimate the percent porosityof each sample as described below:1. Initial mass of the sample = M o M2. M s s of the saturated sample = max M M3. Mass of Pores = max - o 3 Since the density of water (w/v) is 1 g/cm at 4 ° C, this value can also be considered the volume of the pores (V p ).4. Measure the apparent volume of the saturated sample by placing it in a beaker containing a known quantity of water. According to Archimedes Principle (see definition in Ex. 11), the quantity of water displaced is equal to the apparent volume (V a ).5. The % Porosity = % Voids An estimate of the % Porosity (assuming that all pores are accessible and the sample is saturated, i.e. assuming a good relationship between porosity and permeability) can, therefore, be obtained by the following:50 51
  31. 31. Ex. 13 POROSITY IN SOLIDS: HYDROSTATIC WEIGHING Ex. 13 (continued) equal to the mass of the body less the mass of waterAIM displaced.The aim of this test is to measure the total porosity of a material by When a body floats in water, the mass of water displacedmeans of its apparent and real densities (a "fluid displacement" is equal to the mass of the body, whether it is totally ormethod). This can be useful for assessing the extent of some types of partially immersed.stone decay and for determining the extent to which pore space has beenfilled by an impregnation treatment. CALCULATIONSDEFINITIONS Porosity ε is generally calculated by means of the following formula: PaPorosity E: The fraction of the total volume of a solid that is occupied ε = 1 - ____ where: by pores (more simply, the empty spaces or voids in a solid mass). The % Porosity = % Voids. PrPermeability: The ability to transmit liquid or gas from one place to P a = apparent density as defined above AND another. P r = real density as defined above.Capillarity: The attraction between molecules, both like and unlike, which results in the rise of a liquid in small tubes or fibers or in the wetting of a solid by a liquid. EQUIPMENTPorosimetry: The study of pore-size distribution. The volumetric distribution of the open pores, assumed to be of circular Oven, balance, tray. section, according to their size (radius or diameter), usually expressed as a percentage of the mass of the sample. This property is related to capillarity, which increases in PROCEDURE inverse proportion to the pore diameter (i.e. capillarity is greater where there are smaller pores). 1. Samples can have the form of a cylinder, cube, or prism. Their 3 volume must be at least 25 cm .Apparent Volume (V a ): The volume of a sample including the pore space. 2. Dry the samples at 60 ° C ± 5 ° C until constant mass. (The constantReal Volume (V r ): The apparent volume of the sample minus the volume mass is reached when the difference between two successive of its pore space accessible to water. weighings, at an interval of 24 hours, is not more than 0.1 % of the mass of the sample.) The drying temperature of 60 ° C is chosenApparent Density (pa): The ratio of the mass to the apparent volume of instead of a higher one to avoid deterioration of any organic the sample expressed in kg/m . 3 materials used to treat the stone. 3. Weigh the samples: M 1 (in grams).Real Density (pr): The ratio of the mass to the real (or impermeable) 3 volume of the sample expressed in kg/m . 4. Place the samples in a tray, cover with tap water at 15-20 ° C, and leave immersed for 24 hours.Principle of Archimedes: If a solid body is wholly or partially immersed in a liquid, the upthrust force (or buoyancy force) acting 5. Take each sample out of the tray and weigh it immersed in water: on the body is equal to the weight force of the liquid that is, suspended by a wire hook from the plate of the balance displaced by the body, and acts vertically upwards through into a container of water (hydrostatic weighing). Let M 2 (in grams) the center of gravity of the displaced liquid. The apparent be the mass of the sample immers e d in water. Quickly wipe the mass of a solid body immersed in water is therefore previously immersed sample with a damp cloth (in order to remove surface moisture) and then weigh it in air on the plate of the balance. Let M 3 (in grams) be the mass of the sample saturated with water.52 53
  32. 32. Ex. 13 (continued)Ex. 13 (continued)RESULTS 3− The volume of the pores (Vp), in cm , is expressed by M3 - M1 (water density at 20°C considered to be 1.0).− The apparent volume is: M3 - M2 (In the case of stones with large pores, the apparent volume is determined by measuring the dimensions of the sample. A gauge with a precision of 0.1 mm should be used.)− Record your results in the data sheet on the next page.− BIBLIOGRAPHY Rossi-Doria, Paola. Some laboratory tests on stone. Course notes for the ICCROM Scientific Principles of Conservation Course, 1983. Unesco, RILEM. Bulk and real densities. In: Deterioration and protection of stone monuments: experimental methods. Volume V, Test I.2.International Symposium, Paris: Unesco, 1978. 55 54
  33. 33. Ex. 14 MOVEMENT OF SALTS Ex. 15 SALT CRYSTALLIZATIONAIM AIMThis simple experiment illustrates how soluble salts are This test is useful to assess the success of a preservationtransported by water and how they damage porous materials. treatment. It can also be used as an artificial weathering test.Water-soluble salts can originate from the soil, the air, or fromthe materials themselves. They are transported inside thematerials by water capillarity or by other means. When water EQUIPMENT/CHEMICALSevaporates, the salts come toward the surface of the material andcrystallize (change from liquid state to solid state) on the Oven, beaker, rod, tray, cover for tray, clamps, sodium sulfatesurface or close to it. These salts, in crystallized form, cause decahydrate (Na 2 SO 4 • 10H 2 0), silica gel.breaking and spalling of the surface. PROCEDUREEQUIPMENT/CHEMICALSOven, tray, distilled water, sodium sulfate decahydrate 1. Use both treated and untreated samples of porous building(Na 2 SO 4 .10H 2 0). materials. 2. Dry the samples in the oven at 60°C for 24 hours and then place them in a dessicator with silica gel to cool.PROCEDURE1. Dry a sample in the oven for 24 hours at 60°C. 3. Weigh the samples (M o ) when they are cool, and then totally immerse them in a 14% solution of sodium sulfate decahydrate.2. Weigh it: (M o ). A saturated solution can be used for stones of greater durability or to simulate harsher weathering conditions.3. Put it in a tray containing 1 cm of a 10 % solution of sodium 4. After the samples have been immersed for 24 hours, dry them for sulfate decahydrate in distilled water and let the sample 24 hours in the oven and then cool in the dessicator. Weigh each soak for a minimum of two weeks. sample (M n ) and then immerse again in the solution.4. Maintain the solution at constant level, and observe the 5. Continue the drying - immersion cycle (weighing the samples each crystallization of salt day by day. time) until there is evidence of macroscopic deterioration or until the samples are completely destroyed.5. Take the sample out of the solution. Dry it in the oven for 24 hours and then weigh it: (M 1 ). BIBLIOGRAPHY6. The quantity of salts absorbed is M I - M o . Record all results below. ICCROM, Scientific Principles of Conservation Course, Course exercises. Rossi-Doria, Paola. Some laboratory tests on stone. Course notes for the ICCROM Scientific Principles of Conservation Course, 1983.BIBLIOGRAPHYMassari, G. Humidity in monuments. Rome: ICCROM, 1971. 57Mora, P. Causes of deterioration of mural paintings. Rome:ICCROM, 1974.56
  34. 34. Ex. 16 QUALITATIVE ANALYSIS OF WATER-SOLUBLE SALTS AND Ex. 16 (continued) CARBONATES d) Another possible origin of sulfates is microbiological. In brief, there are certain types ofAIM/INTRODUCTION micro-organisms capable of metabolizing reduced forms of sulfur and oxidizing it to sulfates, as wellThe presence of white efflorescence on the surface of masonry as others which pro-duce sulfides instead. Theseis always an indication of chemical deterioration processes "sulfur bacteria" are often present on exposed stone,resulting from the reaction of three components: the materials especially calcareous types. Since there is a strictthemselves, water, and polluting compounds present in the water analogy between calcareous stones and mortars basedor the atmosphere. (A fourth component can be contributed by on calcium carbonate, it is logical to assume thatmicro-organisms.) these bacteria could also develop in plasters and mortars.The deterioration products resulting from the reactionbetween these three components are water-soluble salts, e) The most important source of sulfates, however, isprincipally sulfates, chlorides, nitrites and nitrates. Under atmospheric pollution. The burning of hydrocarbonscertain conditions, calcium carbonate (a normal component of leads to the transformation of the sulfur they containmortars and calcareous stones), practically insoluble in into sulfur dioxide (SO2) emitted into the atmospherewater, can also be a deterioration product, usually appearing as a gas.in the form of a surface incrustation. Reacting with oxygen (02) sulfur dioxide(SO2)Qualitative analysis of soluble salts (from a stone or mortar becomes sulfur trioxide (or sulfuric anhydride, S03).sample) furnishes information about the types of ions(sulfates, chlorides, etc.) present in the sample and gives This last product (SO3) reacts with water (H20) to forman indication of the maximum quantity of single ions present. sulfuric acid (SO3 + H2O = H2SO4) which attacks theSuch information provides some clues as to the type of calcium carbonate (CaCO3) and transforms it intodeterioration in progress and its causes. calcium sulfate (CaSO4).Origins of the Most Common Salts All these processes can happen in the wall. Alternately, the sulfuric acid can form in the air and(1) Sulfates then react with the calcium carbonate (CaCO3) of the wall. The sulfates most commonly found in masonry are hydrated calcium sulfate (gypsum, CaSO4 2H20) and, more rarely, A third possibility is that the sulfuric acid formed magnesium sulfate (MgSO4). in the air is neutralized by basic substances such as ammonia (NH3), forming ammonium sulfate ((NH4)2SO4), The possible origins of such salts are the following: or by calcium carbonate present as atmospheric dust, forming calcium sulfate (gypsum, CaSO4). In a polluted a) Sulfates are present in agricultural land and can environment, these sulfate solids can constitute 20 enter a wall through capillary action. to 30% of the dust in the atmosphere. b) Sea water, in addition to chlorides, contains small As a final possibility, studies have shown that sulfur amounts of sulfates, especially magnesium sulfate. dioxide (SO2) can be absorbed directly or as sulfurous Sea spray can thus deposit sulfates on a surface. acid (H2S03). This leads to the formation of calcium sulfite (CaSO3 2H20 ) which oxidizes to sulfate. c) Some materials used in the preparation of mortars and plasters can contain small quantities of sulfates as The processes described above are summarized in the impurities. These can be dissolved in water present chart on the following page: in the masonry wall and brought to the surface as efflorescence. Erroneous use of substances like gypsum for restoration can lead to the presence of sulfates. 5958
  35. 35. Ex. 16 (continued) Atmospheric pollution can also produce nitrates. The combustion of hydrocarbons, in addition to creating sulfur dioxide (SO 2 ), also produces various organic molecules and nitrogen oxides. These nitrogen oxides are extremely dangerous to animal and vegetable life because, in the presence of ultraviolet light, they react with oxygen and the organic molecules present in the polluted atmosphere, forming ozone and organic radicals. The ozone, inturn, oxidizes these radicals to aldehydes and the sulfur dioxide(SO 2 ) to sulfur trioxide (SO 3 ). This particular mix of substances produces a dangerous fog called "photochemical smog" which can be found in areas having severe pollution and long periods of strong sunlight (eg. Los Angeles or Naples). The nitrogen oxides, through a series of complex reactions, form nitric acid (HNO 3 ) which, reacting with calcium carbonate (CaCO3), leads to the formation of calcium nitrate (Ca(NO 3 ) 2 • 4H 2 O). (2) Carbonates Calcium carbonate is a normal constituent of both calcareous stones and of mortars (where it is formed by the carbonization of lime). Unlike the other salts of efflorescence, calcium carbonate is practically insoluble in water. It can, however, be dissolved as bicarbonate when the water contains a high enough quantity(2) Chlorides of carbon dioxide (CO 2 ). These salts (especially sodium chloride (NaCl) and calcium Carbon dioxide is a gas that is normally present in the chloride (CaC1 2 )) are principally deposited on a wall by sea atmosphere. Its concentration can increase, however, under spray. particular conditions - such as in the case of certain industrial activity or when a large number of people occupy a closed room. Chlorides can also be the result of impurities in the materials If dissolved in water present in a humid wall, carbon dioxide (particularly the sand) used to prepare mortars and plasters. forms carbonic acid (H 2 CO 3 ) which reacts with calcium carbonate (CaCO 3 ), forming the more soluble bicarbonate. Finally, some types of industrial activity, like the combustion of certain kinds of pit-coal, can result in the presence of There is thus an equilibrium between these various substances gaseous hydrochloric acid (hydrogen chloride, anhydrous (HC1)) (carbonates, CO 2 + water, bicarbonates) which leads to the in the atmosphere. production of soluble bicarbonates when there is a high concentration of carbon dioxide (CO 2 ).(3) Nitrites and Nitrates When a wall begins to dry, bicarbonate salts in solution come to the surface. As evaporation takes place, the previously Nitrites are not often found in walls because they oxidize established equilibrium shifts in favor of the formulation of rapidly into nitrates. calcium carbonate which, being practically insoluble, is rapidly deposited on the surface. The decomposition of nitrogenous organic material produces nitrites. Thus, nitrites might be present where there is infiltration of sewage water or in the vicinity of old burial sites. In general, however, nitrates are much more frequent. They can have the same origin as nitrites, but can also come from the earth 61 in agricultural regions. 60